hrtimer: Make enqueue mode check work on RT

hrtimer_start_range_ns() has a WARN_ONCE() which verifies that a timer
which is marker for softirq expiry is not queued in the hard interrupt base
and vice versa.

When PREEMPT_RT is enabled, timers which are not explicitely marked to
expire in hard interrupt context are deferrred to the soft interrupt. So
the regular check would trigger.

Change the check, so when PREEMPT_RT is enabled, it is verified that the
timers marked for hard interrupt expiry are not tried to be queued for soft
interrupt expiry or any of the unmarked and softirq marked is tried to be
expired in hard interrupt context.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/hrtimer.h

@@ -107,6 +107,8 @@ enum hrtimer_restart {
  * @state:	state information (See bit values above)
  * @is_rel:	Set if the timer was armed relative
  * @is_soft:	Set if hrtimer will be expired in soft interrupt context.
+ * @is_hard:	Set if hrtimer will be expired in hard interrupt context
+ *		even on RT.
  *
  * The hrtimer structure must be initialized by hrtimer_init()
  */
@@ -118,6 +120,7 @@ struct hrtimer {
 	u8				state;
 	u8				is_rel;
 	u8				is_soft;
+	u8				is_hard;
 };
 
 /**

kernel/time/hrtimer.c

@@ -1107,9 +1107,13 @@ void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 
 	/*
 	 * Check whether the HRTIMER_MODE_SOFT bit and hrtimer.is_soft
-	 * match.
+	 * match on CONFIG_PREEMPT_RT = n. With PREEMPT_RT check the hard
+	 * expiry mode because unmarked timers are moved to softirq expiry.
 	 */
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
 		WARN_ON_ONCE(!(mode & HRTIMER_MODE_SOFT) ^ !timer->is_soft);
+	else
+		WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard);
 
 	base = lock_hrtimer_base(timer, &flags);
 
@@ -1288,6 +1292,7 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
 
 	base += hrtimer_clockid_to_base(clock_id);
 	timer->is_soft = softtimer;
+	timer->is_hard = !softtimer;
 	timer->base = &cpu_base->clock_base[base];
 	timerqueue_init(&timer->node);
 }